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I am looking to implement the zk-SNARK capabilities of Ethereum to allow a user to prove that they have all the components required ('a', 'b', 'c', 'd') to create a publicly known hash 'x'. My general problem can be defined as:

def main(x):
    sha3(a, b, c, d) == x
    return 1

I understand that there are two options to use when it comes to converting this general form program into a QAP and subsequent verification: ZoKrates (https://github.com/JacobEberhardt/ZoKrates) and libsnark (https://github.com/scipr-lab/libsnark).

Would anyone be able to help in guiding me through the steps to convert this into a workable piece of code:

  1. Constructing the circuit either using ZoKrates or libsnark
  2. Generating the proving and verifying key
  3. Generating proofs
  4. Verify the proof in Solidity

The documentation / practical examples are fairly limited so will appreciate any help that can be given.

  • Just FYI, libsnark has a built in SHA256 gadget, but no SHA3 gadget so you may want to consider sha256 as the hash. – Tjaden Hess Jul 17 '18 at 18:22
  • I see, very helpful! Have you used this before? – MSM Jul 18 '18 at 10:53
  • Yes, but I don't have any public code to demonstrate it, unfortunately. I can say that it is very helpful to walk through the ZoKrates code to see how libsnark is translated to Solidity, then duplicate that yourself – Tjaden Hess Jul 18 '18 at 14:01
  • This should be reopened, since there are concrete tutorials & solutions to this now (at least with SHA256) – ivicaa Jan 12 '19 at 17:33